The invention relates to a process for the preparation of ethanedinitrile from hydrocyanic acid.
Ethanedinitrile (cyanogen, (CN)2) is a stable, colorless gas which was first prepared in the laboratory in 1815 by thermal decomposition of silver cyanide. Due to its reactivity ethanedinitrile is a promising building block for the synthesis of organic compounds as reviewed by Roesky and Hofmann in Chemiker Zeitung 1984, 7-8, 231-238. It is also useful as a fumigating agent as shown in U.S. Pat. No. 6,001,383 and WO2005/037332. Furthermore, ethanedinitrile shows promise as an active ingredient in rocket propellant systems.
In known processes ethanedinitrile is formed from hydrocyanic acid in the presence of oxygen, nitrates and a copper catalyst.
In U.S. Pat. No. 3,135,582 there is disclosed the preparation of ethanedinitrile by reacting oxygen and a nitrogen oxide with hydrocyanic acid in the presence of a catalyst at a temperature from 100 to 1000° C.
In U.S. Pat. No. 3,949,061 there is disclosed the preparation of ethanedinitrile by reacting hydrocyanic acid in an aqueous solution in the presence of elemental oxygen, copper nitrate.
In U.S. Pat. No. 3,769,388 there is disclosed oxidizing hydrocyanic acid in the presence of oxygen, a substantially anhydrous liquid medium, a catalytic amount of silver, ruthenium or mercury and a nitrate.
In U.S. Pat. No. 3,494,734 there is disclosed reacting hydrocyanic acid with nitrogen dioxide in the presence of cupric ion as a catalyst.
In DE 1163302 A there is disclosed the oxidation of hydrocyanic acid in the presence of cupric salts in strongly acidic solutions, whereas in the examples and the specification the oxidation is carried out at about pH 2.8. According to the examples the reaction is carried out in the presence of an ammonium salt and elemental oxygen as well as an additional reagent to activate the elemental oxygen.
Riemenschneider, W. discloses in Chemtech 1976, 658-661 that it is advisable to use a slight excess of oxygen in the reaction of nitrogen dioxide with hydrocyanic acid.
Until today the available processes for the preparation are not satisfactory regarding yield and selectivity. Also, the recovery of ethanedinitrile from the effluent gas is difficult, particularly in the presence of excess nitrogen dioxide.